|You are not going to get it. MAC address is part of the Ethernet protocol and is only used with a Local Area Network. The URL is part of the TCP/IP protocol which is what the Internet runs on.|
Once you are past your ISP if the remote computer is using PPPoEthernet or the users router if they are using PPPoATM, MAC addresses are discarded as they are no longer needed. MAC addresses are not transmitted over the Internet.
To discover a computers MAC address you would have to be on the same Local Area Network as they are in which case you wouldn't be needing a URL.